In prior art it is known to deactivate cylinders in order to improve fuel efficiency and reduce emissions for internal combustion engines. The existing solutions may operate, and have their highest efficacy, at low engine load levels. One of the typical solutions is to deactivate half of the number of cylinders in an engine by deactivating both the intake and exhaust valves for those cylinders. By deactivating both the intake and exhaust valves the cylinder becomes fully deactivated. Such cylinder deactivation significantly decreases the fuel consumption and thereby the CO2 emission levels at certain load levels for internal combustion engines. Although the effect is only present at a limited RPM range cylinder deactivation as presented by the prior art has a positive overall effect on for example vehicles fuel consumption.
There are mainly two problems that commonly are addressed by cylinder deactivation systems which both affect the fuel consumption for internal combustion engines. The first problem is excessive amount of cylinder volume at certain RPM levels and load levels creating pumping losses when air is dragged into or exhaust are pushed out of the cylinders. The second problem is the relative slow combustion and heat release on low load levels. Cylinder deactivation addresses both those problems and thereby decreases fuel consumption both by reducing the pumping losses and by and increasing the combustion speed by reducing the cylinder volume.
The problem with pumping losses is present especially at low cylinder pressure and mainly due to the need to draw air in to the cylinders. Furthermore, low pressure in the cylinders of an internal combustion engine is associated with relatively high fuel consumption in relation to the power output due to higher energy required for the combustion reaction. By deactivating cylinders during low load levels, fewer cylinders are required to draw air from the intake manifold which means that the pumping losses as well as the total cylinder volume are decreased. The reduced pumping losses can for example be mainly achieved by keeping both the exhaust and intake valves closed creating a vacuum within the deactivated cylinder either above or below the piston. The vacuum is created above the piston when it moves downwards past its middle point and below the piston when it moves upwards. This creates a state where the piston will always strive to travel towards its middle position, which substantially eliminates the pumping losses.
The conventional solution for cylinder deactivation uses systems with two states where cylinders might be either active or inactive. This is achieved with valves that have either one or two lifting levels each, for example cylinder one might have one lifting level while cylinder two might have two lifting levels. Lifting levels can also be referred to as modes. The lifting levels in such solutions are the same for all cylinders.
Valves with two modes present multiple benefits and is an option presented in prior art. Although two lifting levels is an option it would be beneficial to provide additional lifting levels in order to save even more fuel and decrease emissions. The idea with this is to provide the possibility of utilizing more than two cylinder deactivation states. If valves with more than two lifting levels are used multiple states can be used creating a more dynamic cylinder deactivation.
The problem that prior art solutions encounter when trying to provide more than two states is that equipping each valve with more than two lifting levels present problems with lubricants, seals, cost and space within the engine and the engine bay. For example, in a solution utilizing cam profiles, two lifting levels can be achieved by two cam profiles, which take less space than for example three cam profiles. Thereby, the problem with the current solution is that, although significant fuel savings can be achieved, the methods applicability range, i.e., the RPM range where cylinder deactivation is applicable, is limited due to the limitation to two states and two lifting levels. States are modes of cylinder deactivation that the engine can be set to, i.e., a state of cylinder valve settings that allows for different properties. In order to accomplish more than two states and thereby increase the applicability range the prior art presents solutions utilizing electrical valves. Electrical valves have been used that provides step-less opening options for each valve individually thereby enabling more than two lifting levels and multiple states. However, those solutions are expensive and require advanced engine control units to operate.
With the above problems and solutions in mind it would therefore be advantageous to provide a cylinder deactivation arrangement for an internal combustion engine that can be utilized at an extended RPM range without increasing the complexity of each valve arrangement.